The present invention relates to systems for delivering pressurized gas and, in particular, to a system which switches from one pressurized gas supply to another upon automatic detection of a reduction in pressure in the former pressurized gas supply.
Pressurized gas is used in a number of applications ranging from carbonated beverage dispensers to oxygen systems used in medical and high-altitude environments. Pressurized gas is typically provided in pressurized tanks which release gas at a predetermined pressure through a regulator. When most of the gas has been dispensed from a particular tank, the gas pressure drops to a level below that which is necessary for the intended application. In the case of carbonated beverage dispensers, the dispensed beverages cease to be carbonated, i.e., become xe2x80x9cflat.xe2x80x9d The tank is then typically replaced with a new, full tank of pressurized gas. However, manual tank replacement can be particularly inconvenient. For example, replacing an empty tank of carbon dioxide during lunch at a restaurant may be particularly inconvenient since no personnel may be available to effect the replacement. However, consumers generally prefer beverages carbonated and sales generally drop when carbonated beverages are not available in a particular dining establishment.
To address this problem, valves which automatically detect a reduction in pressure in a first tank and automatically switch to a second tank in response thereto have been developed. U.S. Pat. No. 5,014,733 to Wilson dated May 14, 1991 describes one such valve. The valve of the ""733 patent uses mechanical devices to sense a drop in pressure and switches from a first supply tank to a second, full supply tank in response to the pressure drop.
To automatically trip the switching valve, the relatively high pressures of pre-regulated pressurized gas are required. Therefore, the switching value of the ""733 patent is typically placed between the supply tanks and a regulator. Such generally has two primary drawbacks. The first is that the valve switches to the second supply tank when the first supply tank is not quite empty. Supply tanks generally store gas whose pressure can be as high as 2,500 psi and is regulated to about 100 psi for use in end-user equipment, e.g., carbonated beverage dispenser. Because of imprecision in mechanical switching mechanisms, conventional valves are adjusted to switch from the first supply tank to the second supply tank when the pressure of the gas in the first supply tank drops to about 200 psi. If such conventional valves were configured to switch at a lower pressure, the valve might not switch even if the pressure of the gas in the first supply tank dropped below 80 psi at which end-user equipment might become inoperative. However, even at 200 psi, pressurized gas in liquid form is still present in the first supply tank. Such premature discontinuation of use of the first supply tank results in unnecessary costs and waste since a substantial amount of the gas is never used.
The second drawback of switching unregulated gas is that such conventional switching valves cannot be used with newer, bulk pressurized gas tanks which hold a much larger quantity of pressurized gas at a lower pressure, i.e., typically about 230 psi. Since such conventional valves are configured to switch from the first supply tank to the second supply tank when the pressure of the first tank drops below about 200 psi, such a conventional valve would switch before much of the pressurized gas in the bulk system is used. Such bulk systems require a much more precise switching mechanism.
Conventional switching valves such as that described in the ""733 patent suffer from further disadvantages. For example, conventional valves only switch from the first supply tank to the second supply tank. When the pressure in the second supply tank drops below the threshold pressure, the valve must generally be manually reset to again supply pressurized gas from the first supply tank to the end-user equipment. By this time, the first supply tank which was previously empty hopefully has been replaced with a new first supply tank which is full. However, the user is not informed that the second supply tank is nearly empty and the end-user equipment must generally become inoperative before the user knows to replace the second supply tank. Unfortunately, depletion of the second supply tank is also generally the first time the user is informed that the first supply tank is empty as well. Without careful observation by the user, the user is not informed that the valve has switched from the first supply tank to the second supply tank and, frequently, the first supply tank is not replaced until the second supply tank becomes empty. In this respect, such conventional automatically switching valves are no better than no switching valve at all except that the capacity of the first supply tank can be effectively doubled by adding the second supply tank.
In accordance with the present invention, a smart switch uses a microprocessor to monitor a pressure of gas supplied by a selected one of two or more pressurized gas supplies. When the gas pressure falls below a predetermined threshold pressure, the smart switch decouples the selected pressurized gas supply from down-line equipment using the pressurized gas and couples a different pressurized gas supply to the equipment. In addition, the smart switch, upon detecting the falling gas pressure, communicates the low gas pressure and change of pressurized gas suppliesxe2x80x94along with status of the smart switch itselfxe2x80x94to a remotely located computer system which is sometimes referred to as the host computer. The remotely located computer system then dispatches service personnel to the location of the smart switch to replace the empty pressurized gas supply and to perform general maintenance of the pressurized gas system there.
The smart switch senses regulated pressurized gas such that lower gas pressures are handled. In addition, the measured gas pressure is accurate to within about one-half pound-per-square-inch (psi). Accordingly, the predetermined threshold pressure can be set sufficiently low (e.g., 80 psi) that all pressurized gas in liquid form has been used yet sufficiently high that the equipment using the pressurized gas is still operative. In addition, such a system can effectively monitor gas supplied by large, bulk pressurized tanks which operate at significantly lower pressures than older, smaller, high pressure tanks.
In communicating with the host computer, the smart switch identifies itself by sending identification data and authenticates itself by sending associated passcode data. The smart switch further sends data representing the status of the smart switch include a log of any errors encountered during operation of the smart switch, status of each pressurized gas supply tank controlled by the smart switch, and the version of control firmware used by the smart switch. Once this information is communicated to the host computer, the smart switch enters a server mode in which the host computer issues commands to the smart switch. As a result, a cracker posing as a smart switch is unable to control communications with the host computer to obtain customer information or other sensitive information.
Once the smart switch has entered the server mode, the host computer determines whether any changes must be made to the smart switch. Such changes include new access information, such as a telephone number by which the smart switch contacts the host computer; new identification data for the smart switch; a new passcode for authentication of the smart switch; new service authorization data; and new programming for the smart switch. If any changes are needed, the host computer issues a download command and sends the necessary item to be changed.
The predetermined threshold pressure of the smart switch is field-programmable. Specifically, a service technician causes the smart switch to enter a pressure set-up mode, establishes a desired pressure at the switchable valve monitored by the smart switch, and presses a set button to cause the smart switch to note the pressure. The smart switch stored the measured pressure as the new predetermined threshold pressure at which smart switch determines a pressurized gas supply is empty.